1. Field of the Invention
The present invention relates to a stack type evaporator for use in the car cooling system or the like, and more particularly to a stack type evaporator which comprises a plurality of plate-shaped tubular elements each having inner paths for coolant, wherein a plurality of air paths are defined through and by a fin member interposed between one tubular element and the next.
2. Description of the Prior Art
In general stack type evaporators for the uses mentioned above comprise tubular elements whose inner paths for coolant are in fluid communication with each other in such a state that a coolant circuit is formed between an inlet and an outlet of the coolant. A mist of the coolant enters the inlet and flows through the circuit so that heat exchange takes place between the coolant and the air passing through the air paths The coolant is thus gradually evaporated to become a gas which then flows out of the evaporator though the outlet.
FIG. 12 shows one of the known tubular elements (such as those disclosed in Japanese Utility Model Publication Sho. 53-32375) which has one end portion formed with a delivery header 10a and a return header 10b. A coolant stream circuit is formed such that coolant flows through the delivery header 10a into the inside of said tubular member, advances toward the other end portion thereof where it makes a U-turn, and then flows back to the return header 10b. Such a coolant stream within the circuit is made turbulent by the existence of many protruding inner ribs 70 possessed by each of dish-shaped core plates 60 which are secured to each other at their peripheries so as to form a space for the coolant circuit therebetween, the ribs 70 being disposed within the space. Said ribs 70 are oblique with respect to the flow direction of coolant stream, and as shown by rigid lines and phantom lines in FIG. 12, each rib 70 of one core plate 60 and each corresponding rib 70 of the other core plate firmly coupled with the one core plate intersect one another. However, the U-turn of the coolant stream within said circuit of the tubular element is likely to cause a "channel" or uneven flow of coolant in the circuit, thereby bringing about a substantial decrease in the effective heat transfer surface.
It is further to be noted that the mutually intersecting ribs 70 disposed oblique to the direction of coolant flow are disadvantageous in that pressure loss of coolant increases unfavorably in the tubular elements near an outlet port of the evaporator, in spite of lowered efficiency of heat transfer due to the increasing ratio of gas in the coolant which is getting near the outlet. Such a disadvantage depreciates the value of an expected advantage, that is an improved heat transfer efficiency, which will be obtained owing to violent turbulence of coolant in the tubular elements disposed near an inlet port of the evaporator.